Each leaf of a mitre gate has a side for hinging with the lock wall and a side where the junction is done with the other leaf of the mitre gate in the middle of the stream of water. A leaf for a mitre gate of the prior art comprises a generally flat skin plate and two uprights respectively located on the hinge side and the junction side of the skin plate. The skin plate is intended to bear pressure exerted by the liquid situated upstream of the mitre gate, which causes two forms of mechanical stress. The lateral ends of the leaf, the hinge side and the junction side, transmit compression forces. Between these two lateral ends, the leaf works in flexion and compression, the flexion work being predominant in the central part of the leaf. Between these two lateral ends, the skin plate works in flexion. The structure of the leaf consists of horizontal beams and vertical and horizontal stiffeners, which are made up of thin plates secured to one another.
However, in a leaf for a mitre gate of the prior art, the compression forces to which the skin plate is subjected are transmitted from one end of the leaf to the other along lines of force that alternatingly pass through said horizontal plates and vertical plates. This alternation causes relatively high stress concentrations between these components, in particular the horizontal beams and the two uprights on the one hand, and the vertical stiffeners on the other hand. However, such stress concentrations decrease the fatigue life, and therefore the useful life, of the leaf.